EP4173028B1 - Method and device for bonding substrates - Google Patents

Description

The invention describes a substrate holder, a device and a method for bonding two substrates according to the independent claims.

The state of the art shows a large number of different substrate holders. Especially in fusion bonding, the substrate holders are becoming increasingly complicated and sophisticated in order to meet the ever increasing requirements of the bonding process. In the publication WO2012083978A1 A substrate holder was mentioned that can compensate local and/or global distortions through active control using thermo-, piezo- or fluid elements. The substrate holder of the publication WO2013023708A1 shows ways to avoid contamination of the back of a substrate as much as possible, as well as a method for detaching the substrate by targeted control of the fixing elements. The publication WO2017162272A1 shows a substrate holder that has several fixing zones that are distributed symmetrically over the substrate holder and can be switched individually. The publication WO2018028801A1 shows a method to fix a substrate not radially symmetrically, but uniaxially and also to release it in its uniaxial curvature. In the publication WO2014191033A1 discloses a substrate holder whose surface is curved or bendable in order to provide a substrate fixed thereon with an inhomogeneous curvature before and/or during bonding. The publication WO2014191033A1 mentions in particular on page 9 that the adjustable curvature is not a homogeneous, i.e. an inhomogeneous, curvature. With each new generation of substrate holders, better and faster bonding results have been achieved, but these can still be optimized through further technological improvements. It has now been recognized that the two substrate holders are of crucial importance in a bonding process. In particular, the control of a continuous bond wave in a fusion bond is extremely important for a correct bonding result. The control is also influenced in particular by the way in which the substrates participating in the bonding process are curved. Another similar state of the art is US2020013643 refer to.

One of the problems with the prior art is that not only the surface on which the substrate is fixed is curved in a well-defined manner, but that other components of the substrate holder are also mechanically influenced, in particular curved, during the curving process. In terms of construction, a substrate holder with a solid construction would be possible, i.e. a construction consisting of very thick and massive parts that have a high bending resistance. However, some substrate holders have to be small and compact, i.e. relatively delicate, and therefore necessarily have a relatively low bending resistance. This low bending resistance then causes a slight, unwanted, elastic deformability of some parts of the substrate holder that should not actually be curved. These elastic deformations and curvatures act on the surface on which the substrate is fixed, the fixing plate surface, and thus influence the curvature of the substrate. It must be mentioned that the resulting elastic deformations naturally only occur in the nanometer or micrometer range, but elastic deformations of this magnitude are already sufficient to have a negative effect on the fixed substrate and its curvature.

It is possible to create a homogeneous, curved fixing surface on a substrate holder by milling, grinding, polishing, etching and lapping processes, so that the substrate fixed to it also has a homogeneous curvature. However, this fixing surface is static and could not change the curvature. On the other hand, it would be possible to build a substrate holder that can curve the fixing surface, as in the publication WO2014191033A1 However, with these substrate holders it is very difficult to specifically adjust the curvature of the fixing surface and therefore the curvature of the substrate as a function of location, and in particular to keep it constant. Above all, setting a homogeneous curvature of the substrate is very difficult, impossible or at least not reproducible.

The object to be achieved by this invention is to eliminate the disadvantages of the prior art and in particular to provide an improved substrate holder, an improved device and an improved method for bonding.

This object is achieved with the features of the independent claims. Advantageous further developments of the invention are specified in the subclaims. The scope of the invention also includes all combinations of at least two of the features specified in the description, the claims and/or the figures. In the case of specified value ranges, values lying within the stated limits should also be considered as disclosed limit values and can be claimed in any combination.

It is of particular technical importance to design a substrate holder in such a way that it bends a substrate in a targeted, adjustable manner, in particular homogeneously.

The invention relates to a substrate holder for curving a substrate, according to claim 1.

The fixing plate has a front side on which the substrate is fixed and a rear side facing away from the front side. The fixing plate has a width, a length and a thickness. In another embodiment, the fixing plate is designed to be radially symmetrical and is then defined by a radius and a thickness. The width and the length extend in the direction of a fixing plate surface on the front side of the fixing plate on which the substrate is fixed. The thickness extends perpendicular to the fixing plate surface.

Preferably, the thickness of the fixing plate varies, i.e. the thickness is not the same at every point, but the fixing plate is thicker at at least one point of the fixing plate than at another point. Special

Training/preferred forms are described below.

Preferably, it is provided that a homogeneous curvature of the fixing plate or the substrate is adjustable.

The fixing plate is hinged.

Targetedly adjustable means that the value of the curvature can be set. Homogeneous means that with a set value of the curvature, this curvature is the same, i.e. constant, at every position of the fixing plate or substrate, within a negligible error tolerance.

Preferably, the rear side of the fixing plate is shaped in such a way that a homogeneous curvature of the fixing plate results or that a homogeneous, and therefore identical at every location, curvature of the fixing plate or the front side of the fixing plate and thus of the substrate can be set.

In a preferred embodiment, but also as an independent inventive aspect, the substrate holder is designed such that reaction forces and/or moments generated during the curvature of the fixing plate can be compensated by at least one compensation means.

• eine Fixierplatte zur Befestigung des Substrats,
• Krümmungsmittel zur Krümmung der Fixierplatte,

wobei bei der Krümmung der Fixierplatte erzeugte Reaktionskräfte durch mindestens ein Kompensationsmittel kompensierbar sind.As an independent inventive aspect, the invention relates to a substrate holder for curving a substrate, comprising

• a fixing plate for attaching the substrate,
• Curving means for curving the fixing plate,

wherein reaction forces generated by the curvature of the fixing plate can be compensated by at least one compensation means.

The invention further relates to a device, in particular a bonding device, comprising at least one substrate holder according to the invention.

• ein erstes Substrat auf einem ersten, insbesondere erfindungsgemäßen, Substrathalter befestigt wird,
• ein zweites Substrat auf einem zweiten, insbesondere erfindungsgemäßen, Substrathalter befestigt wird,
• die Substrate (7) zueinander ausgerichtet werden,
• mindestens eines der Substrate (7) gekrümmt wird,
• die Substrate kontaktiert werden,

wobei die Krümmung mindestens eines der Substrate bzw. der Fixierplatte gezielt eingestellt wird, bevorzugt homogen ist.The invention further relates to a method for bonding two substrates, comprising the following steps, wherein:

• a first substrate is attached to a first substrate holder, in particular according to the invention,
• a second substrate is attached to a second substrate holder, in particular according to the invention,
• the substrates (7) are aligned with each other,
• at least one of the substrates (7) is curved,
• the substrates are contacted,

wherein the curvature of at least one of the substrates or the fixing plate is specifically adjusted and is preferably homogeneous.

Preferably and as an independent inventive aspect, when the fixing plate is curved, the moments and/or reaction forces generated in the remaining components are either compensated for, but preferably not transferred to the fixing plate at all or only to a small extent.

• ein erstes Substrat auf einem ersten, insbesondere erfindungsgemäßen, Substrathalter befestigt wird,
• ein zweites Substrat auf einem zweiten, insbesondere erfindungsgemäßen, Substrathalter befestigt wird,
• die Substrate zueinander ausgerichtet werden,
• mindestens eines der Substrate gekrümmt wird,
• die Substrate kontaktiert werden,

wobei bei der Krümmung der Fixierplatte die in den restlichen Bauteilen erzeugten Momente und/oder Reaktionskräfte entweder kompensiert, vorzugsweise aber erst gar nicht oder nur in geringem Umfang auf die Fixierplatte übertragen werden. Bevorzugt wird das durch die Verwendung eines Lagers bewerkstelligt, über das möglichst keine bzw. nur sehr geringe Reaktionskräfte und/oder Momente übertragen werden.A further independent aspect of the invention therefore relates to a method for bonding two substrates, comprising the following steps, wherein:

• a first substrate is attached to a first substrate holder, in particular according to the invention,
• a second substrate is attached to a second substrate holder, in particular according to the invention,
• the substrates are aligned with each other,
• at least one of the substrates is curved,
• the substrates are contacted,

whereby the curvature of the fixing plate either compensates for the moments and/or reaction forces generated in the remaining components, but preferably does not affect the Fixing plate. This is preferably achieved by using a bearing through which no or only very low reaction forces and/or moments are transmitted.

It is preferably provided that the fixing plate is thicker in the center than at the edge. This advantageously makes it possible to achieve a particularly homogeneous curvature of the fixing plate and the substrate. The fixing plate is preferably tapered towards the edge. It is preferably provided that the fixing plate is symmetrical to the center.

The essential aspect of the invention is in particular that a substrate can be given a curvature that can be specifically adjusted. In particular, it is possible to create curvatures with a constant, i.e. homogeneous, radius of curvature. Setting a constant curvature is the most preferred inventive procedure for creating a bond. Through an inventive extension and the embodiments, the reaction forces that necessarily always arise according to Newton's third axiom are not absorbed by the components of the substrate holder, which are connected via mechanical coupling to the plate that fixes the substrate, but by a second plate, the compensation plate, which is located inside the substrate holder and is freely (articulated) mounted together with the first plate, i.e. ideally can transmit no or only a negligible moment.

Curvature is the deviation of the shape of an object from an unloaded initial state, particularly characterized by the fact that the position of the center line or center surface of the object changes under load.

Curvature is most easily described as the reciprocal of the radius of curvature for a point on the curve. The radius of curvature at a point is the radius of the osculating circle of the curve through that point. The larger the radius of curvature, the smaller the curvature.

The term "bow" still exists in the semiconductor industry. This refers to the deviation of the center point of the median surface of the substrate of a free, unclamped substrate, especially a wafer, from the median surface of the reference plane. The reference plane is simply a horizontal, flat plane on which the substrate rests clamped. The exact definition can be found in the now outdated ASTM F534 standard.

In the further course of the text, bending line and bending surface are used as synonyms, in particular since the substrate holders according to the invention are preferably drawn in cross section in the figures and therefore only a bending line can be seen instead of a bending surface. The person skilled in the art understands that a two-dimensional surface of a three-dimensional body generally has a bending surface and that only a bending line can be seen or represented in the cross section through such a bending surface.

In the particularly preferred embodiments of the substrate holders and methods according to the invention, a substrate is curved with a constant curvature, ie the curvature is the same at every position of the substrate. The curvature is then also referred to as homogeneous. A constant curvature of a substrate produces particularly optimal bonds between two substrates. Such a curvature can be achieved in particular if one ensures that no reaction forces and/or Moments from other components act on the fixing plate. This is preferably achieved by using a bearing that allows no or only a very small transfer of reaction forces and/or moments.

In general, the curvature can also vary across the substrate. Preferably, however, the curvature is radially symmetrical, i.e. it only changes with the radial position measured from the center of the substrate, but not with the angle. Substrates that form anisotropic curvatures, i.e. whose curvature generally varies with the radius position and the angle, have the property of forming saddle surfaces. However, since the rigidity of the fixing plate according to the invention, in particular of the entire substrate holder according to the invention, is much greater than the rigidity of the substrate and the substrate is fixed to the fixing plate by a fixing element, it can be assumed that the substrate contacts the fixing plate at every point. In this case, the constraint that does not allow the formation of a curvature in the form of a saddle surface would lead to residual stresses in the substrate.

The radius of curvature of a plate or a substrate is greater than 0.01m, preferably greater than 0.1m, more preferably greater than 1m, most preferably greater than 10m, most preferably greater than 100m.

If the radius of curvature is not constant along the bending line or bending surface, the absolute value of the difference between the largest and smallest radius of curvature is less than 1 m, preferably less than 0.1 m, even more preferably less than 0.01 m, most preferably less than 0.001 m, most preferably less than 0.0001 m.

The sheet is smaller than 1000µm, preferably smaller than 500µm, more preferably smaller than 100µm, most preferably smaller than 10µm, most preferably smaller than 1µm.

• Ellipsenabschnitt, vorzugsweise
  • ∘ Kreisabschnitt
• Parabel
• Hyperbel
• Sinus, insbesondere im Wertebereich [0, Pi]
• Negativer Cosinushyperbolicus

Preferably, the embodiments and methods according to the invention can bend a substrate such that the surface in the cross-sectional profile or the bending line can be described by one of the following mathematical functions:

• Ellipse section, preferably
  • ∘ Circular segment
• parabola
• hyperbole
• Sine, especially in the range [0, Pi]
• Negative hyperbolic cosine

• • Ellipsoidenabschnitt, insbesondere
  • ∘ Kreisschalenabschnitt
• • Paraboloid
• • Hyperboloid

The bending surface can then be described in particular by one of the following functions.

• • Ellipsoid section, especially
  • ∘ Circular shell section
• • Paraboloid
• • Hyperboloid

In general, the bending surfaces are therefore the surfaces created by rotating the bending lines.

Of all the above-mentioned possible bending line or bending surface shapes, those which have a homogeneous curvature are the most preferred, i.e. the circular sections or circular shell sections.

This preferred adjustability of a homogeneous curvature is created by a precisely defined and precisely manufactured cavity plate surface of the fixing plate. By producing a defined and precisely manufactured cavity plate surface of the fixing plate, the final shape of the fixing surface of the fixing plate and thus of the substrate is precisely defined. In particular, calculation methods, preferably finite element methods, are used to determine the shape of the cavity plate surface of the fixing plate. The shape of the cavity plate surface of the fixing plate can be described in particular by one of the mathematical functions mentioned above.

• Biegewiderstand der Fixierplatte
• Biegewiderstand des gesamten Substrathalters
• Verwendetes Krümmungsmittel, insbesondere
  • Verwendeter Fluiddruck bei Verwendung eines Fluids
• etc.

However, the actual shape of the cavity plate surface of the fixing plate to be manufactured depends on many factors...

• Bending resistance of the fixing plate
• Bending resistance of the entire substrate holder
• Curving agent used, in particular
  • Fluid pressure used when using a fluid
• Etc.

One idea according to the invention consists in particular in precisely manufacturing only one, single rigid cavity plate surface of the fixing plate and then using this to be able to adjust any curvature on the fixing surface of the fixing plate and thus on the substrate by means of the controllable adjusting means, in particular in such a way that the curvature on the substrate is homogeneous, i.e. the same at every location.

According to the invention, this method of specifically adjustable curvature of a substrate is further supported and improved by creating a precisely manufactured cavity plate surface of the fixing plate, by using at least one compensating means to reduce or completely prevent mechanical reaction when the fixing plate is bent.

It is preferably provided that the at least one compensation means comprises a, in particular curvable, compensation plate.

Preferably, the compensation plate can be bent counter to the curvature of the fixing plate.

It is preferably provided that a preferably sealed gap can be created between the fixing plate and the compensation plate.

It is preferably provided that the curvature of the fixing plate and the compensation plate can be generated by a fluid that can be pressed into the intermediate space.

It is preferably provided that the intermediate space can be generated by a fluid medium, a mechanical adjusting means and/or electrostatic forces. It is preferably provided that the fixing plate and the compensation plate are connected to one another via a, preferably articulated, bearing.

It is intended that the fixing plate and preferably the compensation plate are connected to the other components of the substrate holder via a, preferably articulated, bearing.

Preferably, only a small torque, preferably no torque, can be transmitted via a periphery of the fixing plate and/or the compensation plate. The transmitted torque is less than 1 Nm, preferably less than 10 ^-3 Nm, even more preferably less than 10 ^-5 Nm, most preferably less than 10 ^-7 'Nm, most preferably 0 Nm.

It is preferably provided that the compensation plate has a groove in its outer region, preferably a full-circumferential and closed groove. The distance between the groove and the outer periphery of the compensation plate is less than 50 mm, preferably less than 40 mm, even more preferably less than 30 mm, most preferably less than 20 mm, most preferably less than 10 mm.

It is preferably provided that the compensation plate has a sealing means, preferably a sealing ring, in its outer region, wherein the sealing means is preferably arranged on a, in particular fully circumferential and closed, pedestal. The sealing ring allows the generation of a pressure of more than 1 bar, preferably more than 1.2 bar, even more preferably more than 1.5 bar, most preferably more than 2 bar, most preferably more than 2.5 bar.

It is preferably provided that the at least one compensation means comprises an articulated mounting of the fixing plate. The articulated mounting, which is not capable of transmitting reaction forces and/or moments from the other components of the substrate holder according to the invention to the fixing plate, is therefore itself regarded as a compensation means within the meaning of this disclosure.

Another preferred embodiment of the invention is based in particular on the idea of constructing a substrate holder that has two plates that can be bent in two opposite directions. The curvature is achieved by adjusting means (hereinafter also referred to as curvature means), in particular by using a fluid that is pressed into the space between the two plates. By using two plates, the reaction force generated by the deformation of the first plate does not act on the underside of the substrate holder that holds the first plate, but on the second plate installed according to the invention. This eliminates a harmful and influencing reaction of the reaction force on the substrate holder and thus the substrate. Instead, the reaction force is absorbed (compensated) by the second plate, which can deform freely in the direction of the substrate holder. Furthermore, the invention describes a device, in particular a bonding device, that uses the substrate holder according to the invention on at least one side of the device.

Substrate holder

The substrate holders according to the invention are described in detail below. In particular, it is important to understand all the design measures that can be used to create an adjustable, in particular homogeneous, curvature. Furthermore, design measures are disclosed that can be used to understand the forces and moments acting on the upper plate and how to avoid them.

All substrate holders according to the invention have a fixing surface. The fixing surface is in particular part of a fixing plate. The fixing plate has a cavity surface opposite the fixing surface. The cavity surface is preferably defined according to a mathematical function The shape of the cavity surface results in a well-defined, particularly homogeneous curvature through the use of an adjusting element.

The normal component of a force acting on a lever generates a moment at the lever's point of action. To simplify the description of the invention, the rest of the text will only refer to forces, although the resulting forces also generate moments. The sum of the moments and the sum of the forces must be zero. All consequences resulting from this are therefore also considered to be disclosed.

The substrate holders according to the invention are preferably always designed in such a way that a force bends an upper, first plate, and the counterforce that arises is not absorbed by the components that support or hold the plate, but by compensation components provided specifically for this purpose, in particular a second, lower plate. The second, lower plate must not be mechanically connected to the remaining components of the substrate holder, or only very weakly so, because otherwise it would only be mechanically coupled to the upper, first plate and could transmit a moment. A characteristic feature must be that no or at least only a negligible moment can be transmitted via the periphery, in particular both plates. The plates, as well as some other necessary machine elements, must therefore form as ideal a floating bearing as possible on the periphery, in particular as ideal a joint as possible.

In a special preferred embodiment, the substrate holder according to the invention therefore consists of at least two plates which are curved and, above all, articulated.

In a first specific, preferred embodiment of the invention, the plates themselves are the actuating element that causes their curvature by setting the plates to potential, generating a surface charge and electrostatic forces causing the curvature of the plates. The plates are electrically insulated from one another. Such insulation can consist in the surfaces in the periphery of the substrates being made of a dielectric material or being coated with a dialectical material.

Other parts of the plates, particularly on the surfaces of the plates that face each other, are electric, i.e. electrically conductive. In particular, the entire plates, with the exception of their insulating edge areas, are electrically conductive. Both plates can be set to a potential, particularly a positive one, in relation to ground. It is also conceivable that both plates are set to a negative potential in relation to ground. Because both plates are charged with the same polarity, both plates repel each other. If the plates were not electrically insulated at their periphery, the charges would move to the outer surfaces of the two plates. There would be no charges on the inner surfaces of the two plates facing the cavity and the cavity would be field-free.

Accordingly, the plates would not be able to bend outwards according to the invention. The electrical insulation of the two plates brought to potential is therefore an essential inventive aspect of this very special embodiment. In a special extension of the inventive embodiment, areas of the two plates that are electrically isolated from each other can be electrically conductive and each of these electrically conductive areas can be set to a well-defined electrical potential individually and independently of the other electrical areas. This makes it possible to precisely adjust the repulsion of the plates locally. The finer the segmentation of the electrically conductive areas, the more precise the spatial resolution of the adjustable curvature.

In a second special, preferred embodiment of the invention, the two plates are curved by a mechanical adjusting element located between the plates. The mechanical adjusting element can be operated electrically and/or pneumatically and/or hydraulically. Piezoelectric columns are particularly preferably used as adjusting means. In particular, the use of several such mechanical adjusting elements located in several, in particular symmetrical, positions between the plates is again possible. In this case, each of the adjusting means can preferably be adjusted independently of all other adjusting means.

In a third, special, particularly preferred embodiment of the invention, the plates are curved by a fluid that is introduced, in particular pumped, into an intermediate space. The fluid is a liquid, a liquid mixture, a gas or a gas mixture. Most preferably, the fluid is air. This results in a curvature, in particular a symmetrical curvature, of both plates.

The inventive idea behind the special embodiments of the invention is in particular that the lower plate can expand freely and does not transfer any force and/or moment to the remaining components of the substrate holder, so that the latter is not deformed. In particular, the curvature of the first plate, the fixing plate, and thus the curvature of the substrate fixed to it, should not be caused by a mechanical retroactive moment or a mechanically retroactive force.

plates

The substrate holder according to the invention has in particular at least one plate specially shaped on its rear side. In a special embodiment according to the invention, the substrate holder has two plates.

There are two basic types of plates, the fixing plate and the compensation plate. The fixing plate is the plate on which the substrate to be curved is fixed. The compensation plate is the plate that takes on the inventive effect of absorbing the forces and/or moments of the adjusting means and thus largely prevents mechanical feedback to the other components of the substrate holder. In particular, the bearing of the plates is also largely responsible for ensuring that no forces and/or moments from other components are transferred to the fixing plate.

The space between the two panels is called the cavity. All panels have a cavity panel surface and a second panel surface opposite the cavity panel surface, which is used differently depending on the function of the panel.

The cavity plate surface is always the surface that faces the cavity between the two plates. In a particularly preferred embodiment of the invention, the cavity plate surfaces are specially shaped. In particular, the cavity plate surface of the plate that fixes the substrate has a well-defined shape that has a positive effect on the curvature behavior of the plate and thus on the curvature behavior of the substrate.

If a distinction is necessary between the cavity plate surface of the fixing plate and the compensation plate, these are referred to as cavity fixing plate surface and cavity compensation plate surface. The cavity plate surfaces can have any shape, but can preferably be described according to a function that has already been used to describe the bending line or bending surface. All functions disclosed for the bending line and/or bending surface are therefore also considered to be disclosed for the description of the cavity plate surfaces.

The plate surface that fixes a substrate is called the fixing plate surface. A fixing plate surface can therefore only ever be located on one fixing plate.

1. 1. Mechanische Fixierungen, insbesondere
   1.1. Klemmen
2. 2. Vakuumfixierungen, insbesondere mit
   • 2.1. einzeln ansteuerbare Vakuumbahnen
   • 2.2. miteinander verbundenen Vakuumbahnen
3. 3. Elektrische Fixierungen, insbesondere
   3.1. Elektrostatische Fixierungen
4. 4. Magnetische Fixierungen
5. 5. Adhäsive Fixierungen, insbesondere
6. 6. Gel-Pak Fixierungen und/oder
7. 7. Fixierungen mit adhäsiven, insbesondere ansteuerbaren, Oberfläche handeln.

The fixing plate surface has fixings to fix the substrate. The fixings can be in particular

1. 1. Mechanical fixations, especially
   1.1. Terminals
2. 2. Vacuum fixations, especially with
   • 2.1. Individually controllable vacuum tracks
   • 2.2. interconnected vacuum tracks
3. 3. Electrical fixations, especially
   3.1. Electrostatic fixations
4. 4. Magnetic fixations
5. 5. Adhesive fixations, especially
6. 6. Gel-Pak fixations and/or
7. 7. Fixations with adhesive, especially controllable, surfaces.

The fixations can be controlled pneumatically and/or hydraulically and/or electronically.

Vacuum fixation is the preferred type of fixation. Vacuum fixation preferably consists of several vacuum tracks that emerge from the surface of the substrate holder. The vacuum tracks can preferably be controlled individually. In an application that is more technically feasible, some vacuum tracks are combined to form vacuum zones that can be controlled individually and thus evacuated or flooded. However, each vacuum zone is independent of the other vacuum zones. This makes it possible to set up individually controllable vacuum zones. The vacuum zones are preferably designed in a ring shape. This enables a targeted, radially symmetrical fixation and/or detachment of a substrate from the substrate holder, particularly from the inside to the outside.

In a further improvement, the ring-shaped segmented vacuum zones are again segmented along a ring circumference, so that each vacuum zone is divided into several vacuum zones along the ring circumference. Such embodiments have been described in detail in the publication WO2017162272A1 disclosed.

In a particularly preferred embodiment of the invention, so-called pins are located on the fixing plate surface. The publication WO2015113641A1 mentioned such a structure. Through These pins do not have a substrate lying on the entire surface, but mostly only contact the fixing surface at the pins. This reduces contamination on the one hand, and on the other hand a vacuum can be built up in the spaces between the pins along the entire fixing surface of the fixing plate. In particular, the pins are grouped in the vacuum zones that have already been mentioned. These embodiments were also described in detail in the publication WO2017162272A1 In particular, the grouping of the pins and vacuum feedthroughs into vacuum zones, which are distributed on the fixing plate and, above all, can be controlled individually, is hereby explicitly disclosed and, in connection with the actual inventive idea, represents a decisive improvement of the substrate holder according to the invention.

Although the use of vacuum zones mentioned in the publication WO2017162272A1 , which in particular can each be evacuated or flooded through at least one vacuum hole, is considered to be a special, useful and important extension of the inventive idea, the substrate holders according to the invention are described in the further course of the text with a fixing method in which only a very small number of vacuum holes, in particular in the center, are located on the fixing plate surface.

In the embodiments according to the invention in which the substrate is fixed by means of vacuum fixation, the vacuum between the substrate and the fixing plate surface is preferably generated via vacuum holes that have been drilled along a circle, the center of which is the center of the fixing plate. This makes it possible, when using a substrate holder with pins (pins chuck), to position one of the pins exactly in the center of the fixing plate, which has a proven positive effect on the bonding result. A precise description and illustration can be found in the figure description and the Figures. It is therefore a further feature of the invention to disclose a substrate holder with pins, which has one of the pins exactly below the position at which the first contact between the two substrates occurs. Such a pin below the contact point of the two substrates results in a mechanical stabilization of the substrates at this point. Since the bonding wave begins to run from this point, the coincidence of such a pin with the contact point along a line normal to the fixing plate surface is crucial for a stable start of the bonding wave. The effect of a pin exactly below the contact point can be clearly shown in such a way that the pin below the contact point prevents the substrates from being pushed through at this point and thus creates a stable mechanical starting situation.

The second plate is a compensation plate. The compensation plate preferably has a full-circumference and closed groove in an outer area. The groove ensures that the curvature of the lower plate does not continue all the way to its edge, but mainly to this groove. The groove therefore catches the curvature before it reaches the periphery. This further reduces any small reaction on the substrate holder that may still be possible. If the bearing of the compensation plate on the periphery is so good that no moment is transmitted, a corresponding groove could be dispensed with. Nevertheless, the design of such a groove is actually always useful. The compensation plate preferably also has a sealing agent, in particular a sealing ring. The sealing agent is preferably located on a small, full-circumference and closed platform.

Attachment

All substrate holders according to the invention can be used in a system according to the invention for fixing a lower and/or upper substrate. The substrate holders according to the invention are particularly preferably used in a bonding system for fixing the lower and upper substrate. This particularly improves and optimizes the control of the bond, in particular the fusion bond. By using the substrate holder according to the invention as a top substrate holder, in particular the curvature pin, which has long been used in the semiconductor industry and which initiated the centric curvature of a substrate, is replaced.

The preferred embodiment of a system according to the invention consists in using a substrate holder according to the invention for fixing the upper substrate and a substrate holder according to the invention for fixing the lower substrate.

A special system according to the invention consists of a substrate holder according to the invention on the underside and any other substrate holder not according to the invention. The upper substrate holder preferably has the curvature means known in the prior art, in particular a curvature pin or a nozzle from which a fluid emerges which accordingly curves the upper substrate.

In a special extension of a system according to the invention, the bonder also contains an alignment device (aligner).

If the substrates are transparent to electromagnetic radiation of a certain frequency, observation devices are preferably available to analyse the course of the bonding wave. This not only allows the bonding process to be observed, influenced and, if necessary, aborted, but also the behavior of the bond wave as a function of different parameters. Such an analysis helps to further improve the substrate holder according to the invention.

• Reinigungsmodule
• Schleifmodule
• Ätzmodule, insbesondere
  • o Zum chemischen Ätzen
  • o Zum physikalischen Ätzen
• Plasmamodule
• Beschichtungsmodule

In a special extension of a system according to the invention, the following modules can be connected to the system according to the invention, in particular vacuum-tight

• Cleaning modules
• Grinding modules
• Etching modules, especially
  • o For chemical etching
  • o For physical etching
• Plasma modules
• Coating modules

Such modules are preferably part of a so-called cluster system in which there are vacuum-tight gates between the modules. Preferably, there are also locks between some of the modules mentioned. The modules can be arranged in any order. Preferably, there is a central module in which there is a robot that can transport the substrates between the individual modules. Such a centrally arranged cluster is called a star cluster. It is also conceivable that the modules are arranged in series.

Proceedings

The method according to the invention comprises in particular the following steps. The steps do not necessarily have to be carried out in the order mentioned.

In a first process step according to the invention, a first substrate is loaded and fixed onto a first substrate holder. The first substrate holder is preferably a substrate holder according to the invention.

In a second process step according to the invention, a second substrate is loaded and fixed onto a first substrate holder. The first substrate holder is preferably a substrate holder according to the invention.

In a third process step according to the invention, the two substrates are aligned with each other. The alignment is preferably carried out using alignment marks that are located on the substrate surfaces of the substrates. Corresponding alignment systems, which can also be part of a system according to the invention, in particular a bonding chamber, are described in the publications US6214692B1 , WO2015082020A1 , WO2014202106A1 , WO2018041326A1 disclosed.

In a fourth process step according to the invention, the substrates are roughly brought closer together.

In a fifth process step according to the invention, a targeted curvature according to the invention, in particular a homogeneous curvature, of at least one of the substrates is set using a substrate holder according to the invention. It is also conceivable that both substrates, in particular both with the help of a substrate holder according to the invention. The curvature, which is particularly homogeneous, is made possible by the specially shaped back of the fixing plate. With the specifically adjustable curvature, contact between the two substrates occurs at some point and thus a bonding wave is initiated.

For the sake of completeness, the following note is made. If one of the substrate holders is not a substrate holder according to the invention, it can have a conventional deformation element known in the prior art for deforming the substrate. This substrate holder not according to the invention then naturally has all the negative consequences that are eliminated by the inventive idea of this document. However, it is conceivable that just a single substrate holder according to the invention is sufficient to produce a good bond, so that a conventional substrate holder from the prior art can be used on the other side. The deformation element is then preferably a simple curvature pin. This curvature pin must not be confused with the much smaller pins of a pin substrate holder (pins chuck).

In a sixth process step according to the invention, the substrates are released from the substrate holders in a continuous, targeted and above all controlled manner. It is particularly advantageous if at least the upper substrate holder is not only a substrate holder according to the invention, but the fixations on its fixing surface can also be controlled locally. This is especially possible if the fixations have been grouped into zones, in particular vacuum zones, as described in the publication WO2017162272A1 was revealed in detail.

An essential aspect of the method according to the invention is therefore the specifically adjustable curvature of a substrate with the aid of a substrate holder according to the invention, which is only possible because there is no mechanical feedback to the substrate in combination with a specifically controllable detachment of a substrate from its fixing surface during the advancement of the bonding wave.

Figur 1a

einen Anfangszustand eines Substrathalters im Stand der Technik,

Figur 1b

einen Endzustand eines Substrathalters im Stand der Technik,

Figur 2a

einen Anfangszustand eines erfindungsgemäßen Substrathalters ohne Kompensationsplatte,

Figur 2b

einen Endzustand eines erfindungsgemäßen Substrathalters ohne Kompensationsplatte,

Figur 3a

einen Anfangszustand eines erfindungsgemäßen, erweiterten, Substrathalters mit Kompensationsplatte,

Figur 3b

einen Endzustand eines erfindungsgemäßen, erweiterten, Substrathalters mit Kompensationsplatte,

Figur 4

eine erste erfindungsgemäße Ausführungsform eines erfindungsgemäßen Substrathalters mit Kompensationsplatte,

Figur 5

eine zweite erfindungsgemäße Ausführungsform eines erfindungsgemäßen Substrathalters mit Kompensationsplatte,

Figur 6a

eine dritte, bevorzugte erfindungsgemäße Ausführungsform eines Substrathalters mit Kompensationsplatte in Seiten- und Aufsicht in einem Anfangszustand

Figur 6b

eine dritte, bevorzugte erfindungsgemäße Ausführungsform eines Substrathalters mit Kompensationsplatte in Seitenansicht in einem Endzustand

Further advantages, features and details of the invention emerge from the following description of preferred embodiments and from the drawings. They show in:

Figure 1a

an initial state of a substrate holder in the prior art,

Figure 1b

a final state of a substrate holder in the prior art,

Figure 2a

an initial state of a substrate holder according to the invention without compensation plate,

Figure 2b

a final state of a substrate holder according to the invention without compensation plate,

Figure 3a

an initial state of an inventive, extended, substrate holder with compensation plate,

Figure 3b

a final state of an inventive, extended, substrate holder with compensation plate,

Figure 4

a first embodiment of a substrate holder according to the invention with compensation plate,

Figure 5

a second embodiment of a substrate holder according to the invention with compensation plate,

Figure 6a

a third, preferred embodiment of a substrate holder with compensation plate according to the invention in side and top view in an initial state

Figure 6b

a third, preferred embodiment of a substrate holder with compensation plate according to the invention in side view in a final state

In the figures, identical components or components with the same function are identified by the same reference symbols.

The following two figure descriptions and their associated figures, which show two states of a substrate holder in the prior art, are kept as general as possible in order to illustrate the basic concept. They are as simple a description as possible and are schematic sketches, without any claim to completeness.

The Figure 1a shows a schematic representation of an initial state of a substrate holder 1 in the prior art, the fixing plate surface 3f of which can be curved. The substrate holder 1 has a fixing plate 3, which can be supported in particular via a plate bearing 2, in particular on the periphery. In the present case, the plate bearing 2 is primarily a fixed bearing, which in particular is not designed to be articulated. It would of course also be conceivable for the fixing plate 3 to be mechanically connected directly to the rest of the substrate holder 1. It is important that there is a surface described as the fixing plate surface 3f that can be curved. The fixing plate 3 is therefore designed and/or supported in such a way that it can be curved.

In particular, substrate fixations 4 are located on the plate 3, with the help of which a substrate 7 can be fixed to the plate 3. How the substrate fixations 4 are controlled is important for understanding the Device from the prior art is not relevant and will not be explained in detail here.

The Figure 1b shows a schematic representation of a final state of a substrate holder 1 in the prior art. In this special case, the substrate holder 1 is convexly curved when viewed from the outside because an overpressure is built up in the cavity 5. The overpressure is created by a gas or gas mixture with overpressure in relation to the surrounding atmosphere flowing into the cavity 5 via an actuating means 6, in this special case an opening, a valve or a nozzle. The actuating means 6 can alternatively be a mechanical actuating means. The use of an overpressure is therefore only described here as an example.

In this state, several fundamental problems arise. The first problem is that the curvature of the fixing plate surface 3f, and thus also of the substrate 7, is generally inhomogeneous, i.e. the curvature changes, generally with the location. This is a generally undesirable state. The inhomogeneity of the curvature is difficult to recognize in the figure. This problem is mainly related to the fact that the bearings 2 are designed as fixed bearings, i.e. the number of degrees of freedom is too small or even zero.

Another problem in the prior art is the bearings 2, which are usually designed in such a way that they can transmit reaction forces and/or moments to the fixing plate 3. In particular, the bearings 2 in the prior art are not designed to be articulated. The bearings 2 in the prior art are therefore usually able to transmit a moment.

Another problem is that any actuator 6, which is responsible for the deformation of the fixing plate 3, always has a Counterforce is generated. Generalized and expressed in physical terms, according to Newton's third law, a counterforce is created, normalized to the area, a corresponding counterpressure that bends the substrate holder 1 in the other direction. This undesirable curvature of the substrate holder 1 has a particular effect on the plate bearing 2 and thus also influences the curvature behavior of the fixing plate 3, as well as the curvature of the substrate 7 fixed to the fixing plate 3.

This is related to the problem mentioned above, that in the prior art the plate bearings 2 are designed in such a way that reaction forces and/or moments can be transmitted. Even if a final state is reached in terms of control technology, a reaction can be detected via the substrate holder 1, which is absolutely undesirable, since measurements have shown that this worsens the bonding result to be achieved. It is explicitly mentioned and emphasized that the mechanical feedback effects mentioned do not depend on the type of actuating means 6, in the present exemplary case an opening through which a gas or a gas mixture flows, nor on the existence of a cavity 5.

The actuating means 6 can just as well be a mechanical actuating means, a pin, a piezo column, a bellows or any other actuating means that can bend the fixing plate 3. In these cases there would probably be no corresponding cavity 5. The basic physical law always requires that there is mechanical feedback to the substrate holder.

The following figure descriptions or figures, each showing two states of two substrate holders 1', 1" according to the invention, are kept as general as possible in order to illustrate the basic concept. This is a description that is as simple as possible and contains schematic sketches, without any claim to completeness. The embodiments according to the invention are then described in more detail in further figures.

The inventive idea is again illustrated with the aid of a device in which a fluid is used to generate an overpressure in a cavity 5, which curves the fixing plate 3 on which the substrate 7 is fixed. It is again emphasized that the inventive idea is not tied to the use of a fluid and/or a cavity 5. The inventive aspect could just as well be realized with the aid of mechanical, pneumatic, electrical, piezoelectric actuating means 6, as will be shown and explained later in specific embodiments.

The Figure 2a shows a schematic representation of an initial state of a substrate holder 1' according to the invention with which at least a homogeneous curvature can be set. It is assumed that the substrate holder 1' has such a high bending resistance that the problem of mechanical feedback, the elimination or reduction of which will be described in more detail in later figures, does not yet arise here. An increase in the bending resistance can be achieved very easily, for example, by designing some components of the substrate holder 1', in particular the substrate holder 1' as a whole, thicker. The bearing 2' is important, which is manufactured in such a way that no or only very low reaction forces and/or moments are transferred to the fixing plate 3. In particular, the shape of the cavity plate surface 3h is selected so that a later curvature of the fixing plate 3 produces a well-defined, in particular homogeneous, curvature.

The Figure 2b shows a schematic representation of a final state of a substrate holder 1' according to the invention, with which at least a homogeneous curvature can be set. Even if the substrate holder 1' according to the invention has a higher bending resistance, it must still be slightly curved, albeit only to a small extent, when using an adjusting element 6. However, this curvature is relatively small due to the relatively high bending resistance. Nevertheless, forces and/or moments arise that would be transferred to the fixing plate 3 without the bearing 2'.

The special bearing 2' allows a well-defined, in particular homogeneous, curvature to be set on the fixing surface 3f and thus on the substrate 7, since possible reaction forces and/or moments are not transferred to the fixing plate 7 or are only transferred to a lesser extent. The bearing 2` supports the formation of a homogeneous curvature in addition to the components already made of solid construction. In the special case, an adjusting means 6 is used to adjust the curvature, which is an opening, a nozzle or a valve through which a fluid, in particular a gas mixture, preferably air, is pressed.

The use of a fluid gives the embodiment according to the invention with the specially shaped cavity plate surface 3h particular importance. By using a fluid that exerts a homogeneous and isotropic pressure on the cavity plate surface 3h, a force distribution can be assumed along the cavity plate surface 3h, in which the forces are always normal to the cavity plate surface 3h.

This assumption makes it particularly easy to calculate a suitable shape of the cavity plate surface 3f with the help of numerical simulations, in particular finite element methods, in order to obtain the desired, in particular homogeneous, curvature on the fixing surface 3f, and thus on the fixed substrate 7. Such a special shape of the cavity plate surface 3f improves the formation of a homogeneous curvature of the fixing plate surface 3f and thus of the substrate 7 even further.

The Figure 3a shows a schematic representation of an initial state of a further improved substrate holder 1" according to the invention, with which at least a homogeneous curvature can be set and in which harmful influences of mechanical feedback on the plate holder 2' can be further minimized. Such an improvement according to the invention is particularly advantageous when the substrate holder 1" is constructed relatively thin and has a very low bending resistance.

The mechanical reaction can then no longer be neglected and should at least be reduced, and advantageously completely eliminated, by the improved embodiment according to the invention. The advantages of the specially shaped cavity plate surface 3h will not be discussed here. The substrate holder 1" has a fixing plate 3 and a compensation plate 3' which are supported by a plate support 2'. The plates 3, 3' are designed and/or supported in such a way that they can be curved.

For the sake of completeness, it is mentioned that the plate 3 does not theoretically have to be a separate component, but could be part of the substrate holder 1'. The only important thing is the presence of a fixing plate surface 3f.

However, this would result in boundary conditions that would make it almost impossible to produce a constant curvature of the fixing plate surface 3f. The most preferred embodiment according to the invention therefore provides that the fixing plate 3 represents an independent component. The effect according to the invention therefore consists primarily in the use of a compensation plate 3'.

In the further course of the description of the figures, each embodiment according to the invention is therefore shown with the preferred design solution of two plates. In particular, substrate fixations 4 are located on the fixing plate 3, with the help of which a substrate 7 can be fixed to the fixing plate 3. How the substrate fixations 4 are controlled is not relevant for understanding the device and will not be explained in more detail here. The following figures show how substrate fixations 4, which are designed as vacuum fixations, are controlled.

The Figure 3b shows a schematic representation of a final state of the further improved substrate holder 1" according to the invention. A fluid is pressed into a cavity 5 by an adjusting means 6, in the present specific case an opening, a valve or a nozzle, which leads to a curvature of the two plates 3, 3'. In contrast to the prior art according to Figure 1a There is no curvature of the fixation 2 or other parts of the substrate holder 1' and thus no additional moment is created on the fixing plate 3 and the substrate 7 fixed thereon via the fixation 2. The curvature of the fixing plate 3 therefore only occurs due to the effect of the adjusting means 6.

The compensation plate 3' can therefore be regarded as a kind of "sacrificial plate" whose sole task is to prevent or at least minimize the force acting on the remaining components of the substrate holder 1'. In this specific case, the plates 3, 3' must be sealed, particularly at their periphery. For the sake of clarity, the details, particularly the seal, are not shown in this schematic diagram. The seal is, however, discussed in more detail in a figure of the most preferred embodiment shown later.

In the following figures, the different embodiments according to the invention are discussed and illustrated individually and in detail.

The Figure 4 shows a first, preferred embodiment according to the invention, in which the two plates 3, 3' are set to an electrical potential with the same sign, in particular the same value. In order to prevent the two plates 3, 3' from forming an electrically conductive, self-contained body, the plates 3, 3' must be electrically insulated from one another at their contact points by means of an electrical insulation 14. Otherwise, according to the laws of physics, all charges on the cavity plate surfaces 3h, 3h` that form the cavity 5 would migrate outwards.

The self-contained body would form a Faraday cage and would only allow the storage of charge on the outside. The electrical insulation 14 ensures that the two plates 3, 3', viewed electrostatically, do not form a self-contained, conductive body, but rather a conductive body each. This makes it possible to generate charges on the substrate surfaces that form the cavity 5. The Charges or the two plates 3, 3` themselves, together with the necessary circuit 15, accordingly represent the actuating means 6`.

The Figure 5 shows a second, preferred embodiment according to the invention, in which an actuating means 6" is located between the two plates 3, 3'. The actuating means 6" can be, for example, an electrically and/or pneumatically and/or hydraulically controllable mechanical actuating element. It would also be conceivable to use an electrically controllable piezo column. The actuating means 6" could also be two very strong electromagnets which, when electrically controlled, generate two magnetic fields and repel each other in such a way that the two plates 3, 3' are driven apart. An embodiment would also be conceivable in which two plates are set to the same electrical potential and repel each other through their electrostatic charge.

The Figure 6a shows the third, preferred embodiment of the invention in a side view, a detailed view and a top view in an initial state. This embodiment of the invention is an embodiment described in much more detail from the Figures 3a and 3b The illustration includes (i) the specially manufactured bearing 2', via which no or only very small reaction forces and/or moments can be transmitted, and (ii) the compensation plate 3'.

The importance of this embodiment is based primarily on the fact that a fluid is used to bend the two plates 3, 3', which fluid has an isotropic, ie uniform, force effect on the two plates 3, 3', but in particular the fixing plate 3, due to a static pressure. All of the features mentioned in the Figure 6a can also be used in the previously mentioned and treated substrate holders of the Figures 3 and 4 However, due to the importance of this embodiment, they are described in detail in this figure.

Preferably, the fixing plate surface 3f of the fixing plate 3 is supported or contacted at its periphery via a plate support projection 2'v and the plate surface 3h of the fixing plate 3 via a seal 12. The seal 12 in turn preferably rests on the lower compensation plate 3', in particular on a plate support platform 2'p. The seal 12 seals the peripheries of the plates 3, 3' against each other and still allows the curvature of both plates 3, 3'.

At this point it should be mentioned again that the curvatures are extremely small, i.e. the radii of curvature are very large. A point on any surface of one of the two plates 3, 3' will only move in the z-direction by a few nanometers, micrometers, but in very rare cases by millimeters. Such small curvatures also make it possible to keep such a delicate construction mechanically stable. In particular, the plate bearing projection 2'v can be made very fine.

The substrate 7 is fixed by a substrate fixation 4. In the specific case, the drawing shows that parts of the substrate fixation 4 extend through the cavity 5. These parts are designed to be stretchable. This can be, for example, a hose, a guided pipe or any other line that is able to evacuate the area between the substrate 7 and the fixing plate 3. In particular, there are several exit openings of the substrate fixation 3, which are arranged symmetrically around the center. This makes it possible for a pin 11 to be located in the center of the fixing plate 3, which has a positive effect on the bonding behavior.

The Figure 6b shows the third, preferred embodiment according to the invention in a side view in a final state. The actuating means 6, in this special case a non-centric opening, a valve or a nozzle, pumps a fluid into the cavity 5. The fixing substrate 3 is curved according to the invention. The curvature of the compensation plate 3' preferably takes place up to a groove 13, which has been completely introduced into the compensation plate 3'.

This concentrates the curvature on the central part of the compensation plate 3' and ensures that an even smaller moment and/or force is applied to the plate bearing 2`, which in this case consists specifically of a plate bearing projection 2`v, a seal 12 and a plate bearing platform 2`p (see enlarged view in the Figure 6a ), mechanically. This further structural improvement according to the invention completely prevents mechanical feedback on the fixing plate 3 or minimizes it to such an extent that it is negligible.

List of reference symbols

1,1',1",1‴

Substrate holder

2, 2`

Plate storage

2`v

Plate bearing projection

2`p

Plate storage platform

3

Fixing plate

3'

Compensation plate

3f

Fixing plate surface

3h, 3h`

Cavity panel surface

4

Substrate fixation

5

Cavity/space

6, 6', 6"

Adjusting agent/curving agent

7

Substrat

11

pins

12

Seal, especially sealing ring

13

Groove

14

Electrical insulation

15

Circuit

Claims (11)

1. A substrate holder (1',1", 1‴,1ʺʺ) for curving a substrate (7), comprising

   - a fixing plate (3) for fixing the substrate (7),

   - curving means (6, 6', 6") for curving the fixing plate (3),

   wherein the fixing plate (3) is constituted such that the curvature of the substrate (7) can be adjusted in a targeted manner, and characterised in that the fixing plate (3) is mounted in an articulated manner.
2. The substrate holder (1',1", 1‴,1ʺʺ) according to claim 1, wherein the thickness of the fixing plate (3) is varied.
3. The substrate holder (1',1", 1‴,1ʺʺ) according to at least one of the preceding claims, wherein a homogeneous curvature of the substrate (7) can be adjusted.
4. The substrate holder (1',1", 1‴,1ʺʺ) according to at least one of the preceding claims, wherein the rear side of the fixing plate (3) is formed such a way that a homogeneous curvature of the fixing plate (3) results.
5. The substrate holder (1',1", 1‴,1ʺʺ) according to at least one of the preceding claims, wherein reaction forces generated during the curving of the fixing plate (3) can be compensated by at least one compensation means (3'), in particular a curvable compensation plate (3').
6. The substrate holder (1',1", 1‴,1ʺʺ) according to at least one of the preceding claims, wherein the fixing plate (3) is thicker in the centre than at the edge.
7. The substrate holder (1',1", 1‴,1ʺʺ) according to at least one of the preceding claims, wherein the fixing plate (3) is formed tapered towards the edge.
8. The substrate holder (1',1", 1‴,1ʺʺ) according to at least one of the preceding claims, wherein the fixing plate (3) is formed symmetrical to the centre.
9. A device, in particular a bonding device, comprising at least one substrate holder (1',1", 1‴,1ʺʺ) according to at least one of the preceding claims.
10. A method for bonding two substrate (7), comprising the following steps, wherein:

    - a first substrate is fixed on a first substrate holder (1',1", 1"',1"") according to any one of the preceding claims,

    - a second substrate is fixed on a second substrate holder (1',1", 1‴,1ʺʺ) according to any one of the preceding claims,

    - the substrates (7) are aligned with one another,

    - at least one of the substrates (7) is curved,

    - the substrates (7) are brought into contact,

    characterised in that the curvature of at least one of the substrates (7) is adjusted in a targeted manner.
11. The method according to claim 10, wherein the curvature of at least one of the substrates (7) is adjusted homogeneous.

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